Liquid crystal cells as used in light shutters, displays, and the like have contrast variations depending on the angle at which the liquid crystal cells are viewed. Liquid crystal cells are used as controlled shutters in auto-darkening lenses for welding, e.g., being used in welding helmets, welding goggles, and respirator systems. Exemplary liquid crystal cells used in light shutters are described in the patents mentioned below; other shutters may have similar contrast variations. The contrast variations in a liquid crystal shutter used in auto-darkening lenses may result in blocking transmission of substantially all light or much of the light that is incident on the auto-darkening lens from some directions but may not block as much of the light that is incident on the auto-darkening lens from other directions or angles. A prior approach to reduce light transmission due to contrast variations in a liquid crystal shutter of an auto-darkening lens in the dark state or light blocking mode or condition, has been to design or to tailor the liquid crystal shutter. For example, one approach has been to make the liquid crystal shutter several units thick, e.g., using several liquid crystal shutters in optical series. In such an arrangement the portions of one liquid crystal shutter that tend to provide maximum light blockage for incident light at given angles are oriented to align with portions of another liquid crystal shutter that provide relatively minimum light blockage in a dark state for incident light at such given angles. The increased number of liquid crystal shutters increases the cost, weight, and power requirements for the overall auto-darkening lens using the same.
Auto-darkening lenses (sometimes referred to by the acronym “ADL”) have been used in welding helmets, welding goggles, and the like to protect the eyes of a user or wearer from bright light occurring during a welding process. The auto-darkening lens may have a relatively clear or bright state allowing a relatively maximum amount of light to be transmitted to the wearer's eyes to allow the wearer to see the welding tools, etc., while setting up to do welding. Upon the initiation of welding and continuing of welding, relatively bright light detected by a photosensor associated with the auto-darkening lens will cause operating circuitry of the auto-darkening lens to drive the lens to a dark state to reduce transmission of light to the eyes of the user. If the incident light on the auto-darkening lens is at an angle for which the auto-darkening lens provides suitable light blocking function, the user's eyes will be well protected. However, if the light from the welding process is incident on the auto-darkening lens at an angle at which the auto-darkening lens provides less light blocking effect, the user's eyes will be less protected, as the auto-darkening lens has greater light transmission for light incident at such angle(s). For example, light that is incident on a liquid crystal shutter of an auto-darkening lens at an angle that is perpendicular (normal) to the plane of the liquid crystal shutter may be substantially blocked in the dark state of the light crystal shutter, whereby only a minimal amount of light would arrive at the user's eyes. However, a substantially increased transmission of light through the auto-darkening lens, although in the dark “state,” may occur for light that is incident on the liquid crystal shutter from a different incident angle, for example, approximately 30 degrees down relative to horizontal and angularly toward a corner of the liquid crystal shutter. To adjust the liquid crystal shutter to block the latter light to the same extent of light blockage for the mentioned perpendicularly incident light may require additional drive voltage on the liquid crystal shutter to obtain the same dark state transmission characteristics as for the first-mentioned light that is normal to the liquid crystal shutter. Continued operation of the liquid crystal shutter at the higher voltage when the welding light returns to the mentioned normal or perpendicular direction wastes power.
Other optical devices may be sensitive to the existence of one or more point sources of light and/or to the angle and/or direction at which such light impinges on the optical device. For example, a camera lens may cause spots or other anomalies to appear on an image due to a relatively intense light incident on the camera lens at a given angle, direction and/or location. A point source may cause a wrong light intensity measurement by a camera light measuring system and lead to an over or under exposed image.
It will be appreciated that there is a need to determine the angle, location and direction of incident light generally and of incident light from one or more point sources. There also is a need to distinguish between point sources of light and average, relatively uniform ambient light.
Prior through the lens feedback systems for auto-darkening lenses have detected light transmitted through a lens and have attempted to maintain a given shade number. A problem with such through the lens feedback systems is that there is no reliable or constant light source because the light intensity from a welding arc can vary, for example, due to changes in the voltage at which the welding is carried out, the size of the welding arc, sputtering, etc., and the light transmitted through the auto-darkening lens also may vary as ambient light conditions change. Feedback control to adjust the intensity of light transmitted through the auto-darkening lens also lags (takes time) after a change in light intensity has been detected; and this can reduce accuracy of such through the lens feedback. Thus, such through the lens feedback systems may not have a fixed light intensity starting point about which to base feedback adjustments, e.g., as the light source intensity varies and, therefore, the feedback may not accurately represent the intensity of incident light, the direction from which incident light is impinging on the auto-darkening lens, etc. Similar problems may exist in other optical devices and systems used in a number of light conditions.
In the description herein reference will be made to a lens (also sometimes referred to as “welding lens,” “welding filter,” “shutter,” and the like, and to an automatically darkening lens (sometimes referred to as auto-darkening lens) that is able to operate automatically to control transmission of light. The lens may be a light shutter type of a device that is able to control light transmission without distorting, or at least with relatively minimal distortion, of the light and the image characteristics carried by the light or represented by the light. Therefore, when a person looks through the lens, the image seen would be substantially the same as the image seen without the lens, except that the intensity of the light transmitted through the lens may be altered depending on the operative state of the lens. The lens may be used in a welding helmet, and the lens may be used in other types of devices, such as goggles, spectacles, face masks, e.g., for industry (such as in an industrial plant or to protect outdoor or indoor electrical workers), for dentistry to protect the fact of a dentist in the operative, respirator systems, nuclear flash eye protection devices, and other types of helmets, etc. Such devices usually are employed to protect the face or the eyes of a person, as is known, for example, in the field of welding and in other fields, too. Further, the lenses may be used in various other places to protect workers from bright light that could present a risk of injury. The lenses also may be used in safety eye glasses or in regular eye glasses.
For the purposes of providing eye protection, usually a welding lens provides light blocking characteristics in the visible, infrared and ultraviolet wavelength ranges. The actual ranges may be determined by the components of the lens, the arrangement of those components, and so forth. One example of such a welding lens is U.S. Pat. No. 5,519,522. The lens assembly disclosed In that patent includes several liquid crystal cell light shutters, several plane polarizers, and a reflector or band pass filter, which is able to reflect ultraviolet and infrared electromagnetic energy and possibly also some electromagnetic energy in the visible wavelength range. The several liquid crystal cells, for example, may be birefringent liquid crystal cells sometimes referred to as surface mode liquid crystal cells or pi-cells.
As will be described further below, the present invention may be used in a variable optical transmission controlling device. The device is described in detail with respect to use in a welding helmet. However, it will be appreciated that the device may be employed in other environments and in other devices and systems for controlling transmission of electromagnetic energy broadly, and, in particular, optical transmission. As used herein with respect to one example, optical transmission means transmission of light, i.e., electromagnetic energy that is in the visible spectrum and which also may include ultraviolet and infrared ranges. The features, concepts, and principles of the invention also may be used in connection with electromagnetic energy in other spectral ranges.
Examples of liquid crystal cells and shutters (the terms liquid crystal cell and liquid crystal shutter may be used interchangeably and equivalently herein unless context indicates or implies otherwise, lenses using them and drive circuits are described in U.S. Pat. Nos. 5,208,688, 5,252,817, 5,248,880, 5,347,383, and 5,074,647. In U.S. Pat. No. 5,074,647, several different types of variable polarizer liquid crystal devices are disclosed. Twisted nematic liquid crystal cells used in an automatic shutter for welding helmets are disclosed in U.S. Pat. Nos. 4,039,254 and Re. 29,684. Exemplary birefringent liquid crystal cells useful as light shutters in the present invention are disclosed in U.S. Pat. Nos. 4,385,806, 4,436,376, 4,540,243, 4,582,396, and Re. 32,521 and exemplary twisted nematic liquid crystal cells and displays are disclosed in U.S. Pat. Nos. 3,731,986 and 3,881,809. Another type of liquid crystal light control device is known as a dyed liquid crystal cell. Such a dyed cell usually includes nematic liquid crystal material and a pleochroic dye that absorbs or transmits light according to orientation of the dye molecules. As the dye molecules tend to assume an alignment that is relative to the alignment of the liquid crystal structure or directors, a solution of liquid crystal material and dye placed between a pair of plates will absorb or transmit light depending on the alignment of the liquid crystal material. Thus, the absorptive characteristics of the liquid crystal device can be controlled as a function of applied electric field.
As is disclosed in several of the above patents, the respective shutters may have one or more operational characteristics (sometimes referred to as modes or states). One example of such an operational characteristic is the shade number; this is the darkness level or value of the shutter when it is in the light blocking mode (dark state). Another exemplary operational characteristic is the delay time during which the shutter remains in a dark state after a condition calling for the dark state, such as detection of the bright light occurring during welding, has ceased or detection thereof has terminated or been interrupted. Still another operational characteristic is sensitivity of the detection circuit and/or shutter to incident light, for example, to distinguish between ambient conditions and the bright light condition occurring during a welding operation, and sensitivity also may refer to shutter response time or to the time required for the circuitry associated with the lens to detect a sharp increase in incident light (e.g., due to striking of the welding arc, etc.) and to switch the lens from the clear state to the dark state. Even another characteristic, which may be considered an operational characteristic, is the condition of the battery or other power source for the shutter, such as the amount of power remaining, operational time remaining until the power source becomes ineffective, etc. In the past various of the operational characteristics of such shutters have been adjustable or fixed. Various light sensitive devices have been used in the past to sense light incident on an ADL, such as, for example, photocells, photosensors, light sensors, light sensitive solid state devices, such as light sensitive or photosensitive diodes, photosensors, and other devices (collectively devices to sense light will be referred to herein by those terms and/or by other similar representative terms, all of which are considered equivalent). The controllable shutters (ADLs) may be used in welding helmets, respirator helmets and systems, safety eye glasses, regular eye glasses, goggles, and other devices used to protect the eyes of a wearer or user. Operating circuitry operates the shutter to assume the respective states, and the light sensor senses light conditions and provides an input to the operating circuitry to operate the shutter in response to the sensed light conditions. The photosensor (light sensor) provides an output representative of that light. The light may be in the visible, ultraviolet, infrared, or some other spectrum range or combination of ranges.
In an exemplary auto-darkening lens the sensor is placed at the front of a support structure or housing in which the shutter is mounted or the sensor may be in the support structure (e.g., housing), which is provided with an access opening to allow light to reach the sensor. The location at which the sensor is mounted on or in the support structure may be selected to allow the light sensor to receive incident light that is representative of light, which impinges on the shutter. It is desirable that the intensity of the light incident on the sensor would be representative of the light incident on the shutter. In an auto-darkening lens or other controllable light shutter device used for welding it is desirable to detect light representing the occurrence of welding and to distinguish such light from ambient light.
In electric arc welding, usually welding arcs are fairly bright light and are primarily point sources of light that are relatively small, especially compared to typical ambient light condition and light sources intended to illuminate ambient surroundings. The total amount of light that emanates from a welding arc, though, may vary, for example, depending on the size of the welding arc. For example, for a relatively small welding arc, such as that produced by a ten ampere welding arc process, the amount of light to which a person carrying out the welding process would be exposed (that person sometimes being referred to as a user, wearer or welder in this text for convenience), is about half the light to which that person would be exposed outdoors in bright sunlight, but not looking directly at the sun.
To determine whether incident light on an auto-darkening lens is due to a welding arc, the light sensor and associated operating circuitry for the controllable shutter cannot consider only absolute magnitude of the incident light because if the incident light is “spread out” and is not a point source, e.g., is ambient or is reflected off a relatively large surface, the light would not be due to welding and the eye protection desired for welding would be unnecessary. Protection from light due to welding, for example, emanating from a point source, is desirable because that point source light tends to focus on the retina of the eye and may cause eye damage and/or eye fatigue.
Prior light sensors and associated operating circuitry for controllable shutters have encountered some difficulties in determining whether incident light is from a point source, such as that due to welding, or is from a bright ambient light condition. One reason for this difficulty is the sometimes relatively low signal to noise ratio effect, whereby it is difficult to discern the sensing of a point source of light relative to ambient light conditions.
In some light sensor arrangements several photosensors arranged in a relatively large rectangular array are used to sense light incident thereon, and substantial electronic processing is needed to determine whether the incident light is from a point source. However, since a number of the photosensors are illuminated simultaneously there is a relatively low signal to noise ratio, e.g., ratio of point source light to ambient light, and, therefore, the electronic processing may require a relatively large amount of power and time to determine whether point source light is being detected.
For control of the controllable shutter and/or for other purposes it also is desirable in some instances to detect the location from which incident light due to welding is coming. By detecting the direction of incident light it is possible to control a controllable shutter in such a way to assure that light from that incident direction is suitably attenuated to provide desired protection for the eyes of a welder or the like.
Thus, it will be appreciated that there is a need for accurately detecting occurrence of welding and/or the occurrence of other point light sources or the like.
Dynamic operational range or dynamic optical range is the operational range of the lens between the dark state and the clear state, e.g., the difference between the shade numbers of the dark state and the clear state.
An example of a “welding lens with integrated display and method” is disclosed in U.S. Pat. No. 6,067,129. In the invention disclosed therein the current operational characteristics of the shutter can be displayed and can be selectively changed by operating one or more switches. The switches may be flexible membrane switches, microswitches, or another type of switch.
The present invention is useful for eye protection by an automatic darkening light shutter in a helmet or goggle assembly or in another device, if desired. The switching mechanism for powering the light shutter on and off and/or for selecting operational characteristics may be an integral part of the light shutter and/or frame assembly or other component or portion thereof.
The light shutter, photosensor arrangement and/or control of the present invention may be used in a variety of embodiments and applications. The shutter is adjustable to control light, i.e., to increase or to decrease the amount of the incident light that is transmitted through the shutter. When welding is not occurring, for example, the shutter in a welding helmet may be substantially optically clear or transmissive or at least minimizes its attenuation of light. When welding is occurring, the shutter may be dark or closed to reduce the amount of light transmitted therethrough in order to protect the eyes of the person performing the welding and to maximize his or her viewing comfort. In both cases, though, the image characteristics of the light preferably remain intact. A photosensitive device may be used to sense the intensity of light impinging in the area of the shutter so as to provide an input to a drive circuit for the shutter in order to control opening and closing thereof.
The disclosures of the patents identified herein are incorporated in their entirety by reference.